Caitlyn Jenner 's "devout Christian beliefs" are behind her alleged regret over her transition into a woman, according to a biographer.

Writer Ian Helperin - whose claims have been dismissed as "idiotic" by the reality star's rep - has suggested that the former Olympian's attraction to women is causing internal debate regarding her faith.

He told Mail Online : "Her doubts center not on her identity as a woman, but her devout Christian beliefs about sexuality. Caitlyn remains attracted to women but as a Christian believes same-sex relationships are sinful."

Caitlyn - who came out as transgender in 2015 - has hit out at speculation she regrets her change, and dismissed them as simply "not true".

Caitlyn's rep slammed the claims

In a statement to the New York Daily News , Caitlyn's rep responded: "Not worth commenting on such an idiotic report. Of course it's not true."

It comes after author Halperin told The Wrap: "One source confirmed to me Caitlyn has made whispers of 'sex change regret,' hinting she might go back to being Bruce Jenner."

Moving on from the reports, the star is set to make headlines when she poses completely naked for Spots Illustration.

She is set to pose nude for Sports Illustrated

According to Us Weekly, she will pose wearing just an American flag and her Olympic medal to celebrate the 40th anniversary of her win.

The 66-year-old set a world decathlon record at the 1976 Montreal Summer Games while still known as Bruce Jenner .

A source told Us Weekly: "Caitlyn will wear nothing but an American flag and her Olympic medal. She’s excited about it."